Sure, you can help out your favorite Girl Scout troop by ordering from this year s arriving stash of Thin Mints, Samoas or Trefoils. But you don t have to overpay.

Last month, this former Scout ordered five boxes from a co-worker's daughter and happily tweeted about her haul. One of my Twitter followers responded: Yeah, but Kelli, did you shop around? Prices vary, you know." That's true. Girl Scouts of the USA allows each of the100-plus local councils to set its own price. The Girl Scouts of Kentuckiana charge $3.50 per box; the Gateway council in Jacksonville, Fla., charges $4. (All funds stay with the local council, less the cost of the cookies. By the Northern California council's figures, $3.16 of its $4 price goes toward Girl Scout programs, including 70 cents for the troop that sold that box.)

I didn't shop around because I wanted to support a particular Scout. That's a common reasoning, says Ritesh Saini, an assistant professor of marketing at the University of Texas at Arlington. Most consumers buy kids' fundraiser goods not because the cookie dough is so delicious or the $1 candy bar is the best price around (it's not) but because they see it as helpful. "Purchasing [Girl Scout] cookies is a perfect combination of balancing a vice (consuming something not-so-healthy) with a virtue (having engaged in a socially beneficial behavior)," he says.

Still, it's perfectly acceptable to shop around, especially if you don't have ties to a particular kid. Not a fan of the product being sold? Donate directly or politely decline, says Kit Yarrow, a professor of psychology and marketing at Golden Gate University in San Francisco.

We re featuring valuable coupons and sales each Friday to help you spend less on the items you buy. Found a deal we missed -- or looking for a better price on a specific item? Email me at kgrant@smartmoney.com or send me a tweet @kellibgrant.

1) Spa Finder Deal Days

From March 8-14, participating spas in SpaFinder.com s national network are offering select 50-minute treatments for $50. For example, L Institut Sothys New York is offering its signature body massage, the 60-minute version of which regularly goes for $110. By forgoing 10 minutes, you ll save $60.

SpaFinder gift certificates cannot be used as payment. Spas have been booking the appointments since Feb. 26, so openings may be limited -- or nonexistent for some services. If you re out of luck, there are other spa week promotions later in the year, as well as other avenues to save on spa services.

2) LensCrafters

Through April 3, save 50% off lenses when you purchase frames. The sale includes bifocal and prescription sunglass lenses, but excludes some brands of frames and lenses such as Oakley Authentic and Duralens.

Some companies even offer a grace period through March 15 to spend any leftover FSA funds

3) Dummies books

Through March 29, Borders.com is offering a 30% discount on all the Dummies books, and Amazon.com is cutting prices by 37% on titles priced at $25 or more. Meanwhile, TechBargains.com spotted a coupon-sale combo for the Dummies series. Get extra savings during Dummies Month using Wiley Publishing s $5 mail-in rebate on a Dummies book or audio set purchased for $6.99 or more. The rebate is good on eligible purchases through April 30. By combining the two, you d pay just $1.99 for Spanish Phrases for Dummies, an 80% discount off its regular $9.99 tag.

Mail-in rebates are notoriously hit-or-miss, so make sure to fill out the paperwork carefully.

4) Kohl's

Store cardholders can save 30% on online orders with coupon code MARCH30, good through March 10. Kohl's (KSS) lets you use up to three codes per order, so maximize savings with codes NEW6814 to save an extra 10% and FUN2BMVC for free shipping on all orders. Shop before March 7, and you'll also earn $10 in store cash for every $50 spent.